The present invention relates generally to semiconductor integrated magnetic devices, and more specifically, to a toroidal trench inductor.
When constructing a semiconductor integrated magnetic device using a magnetic film, it is desirable to make the magnetic film sufficiently thick to obtain desirable operating characteristics for a given frequency of operation. However, the thickness of a single magnetic layer that is required for a given operating frequency of the magnetic device may result in the build-up of eddy currents in the magnetic material during operation, thereby resulting in some loss. As such, the magnetic film is typically made sufficiently thin to avoid eddy current losses, but with the tradeoff of lower energy storage ability.
The energy storage of an integrated magnetic device can be increased, however, by building a magnetic structure using a stack of alternating thin magnetic and insulating films, wherein the magnetic layers are separated by a thin insulating layer. In general, the use of multiple layers of magnetic material separated by layers of insulating material serves to prevent the build-up of eddy currents in the magnetic material, while providing an effective thickness of magnetic material, which is sufficient to obtain the desired operating characteristics for a given frequency of operation.
Conventional techniques for building multilayer magnetic-insulator structures include sputtering techniques. In general, a sputtering process includes forming a multilayer stack by alternately sputtering layers of a magnetic material and a dielectric material, patterning a photoresist layer to form an etch mask, using the etch mask to etch the multilayer stack of magnetic-insulating layers and remove unwanted regions of the multilayer stack, and then removing the etch mask. While sputtering can be used to build stacks of magnetic-insulating layers, the material and manufacturing costs for sputtering are high.